Semiconductor device and method of manufacturing semiconductor device

Abstract

Characteristics of a semiconductor device are improved. A semiconductor device includes a sequential stack of a buffer layer, a channel layer, and a barrier layer, and includes a mesa part including a fourth nitride semiconductor layer formed over the stack, and a side part formed on both sides of the mesa part and including a thin film part of the fourth nitride semiconductor layer. Generation of 2DEG is suppressed below the mesa part while being unsuppressed below the side part. In this way, the side part that disables the 2DEG suppression effect is provided on an end portion of the mesa part, thereby a distance from an end portion of the side part to the gate electrode is increased, making it possible to suppress leakage caused by a current path passing through an undesired channel formed between a gate insulating film and the mesa part.

What is claimed is: 
     
       1. A semiconductor device, comprising:
 a first nitride semiconductor layer; 
 a second nitride semiconductor layer formed over the first nitride semiconductor layer; 
 a third nitride semiconductor layer formed over the second nitride semiconductor layer; 
 a mesa part formed over the third nitride semiconductor layer and including a fourth nitride semiconductor layer; 
 a source electrode formed over the third nitride semiconductor layer and on a first side of the mesa part; 
 a drain electrode formed over the third nitride semiconductor layer and on a second side of the mesa part; 
 a gate electrode formed above the mesa part; and 
 a side part formed on at least one side of the mesa part and including the fourth nitride semiconductor layer, 
 wherein the gate electrode is formed above a first a portion of the side part, 
 wherein a second portion of the side part extends to the outside of the gate electrode, and 
 wherein generation of two-dimensional electron gas between the second nitride semiconductor layer and the third nitride semiconductor layer is suppressed below the mesa part while being unsuppressed below the side part. 
 
     
     
       2. The semiconductor device according to  claim 1 , wherein the mesa part includes the fourth nitride semiconductor layer being undoped. 
     
     
       3. The semiconductor device according to  claim 2 ,
 wherein the fourth nitride semiconductor layer includes a first thickness part, and a second thickness part disposed on both sides of the first thickness part and having a smaller thickness than the first thickness part, and 
 wherein the mesa part includes the first thickness part, and the side part includes the second thickness part. 
 
     
     
       4. The semiconductor device according to  claim 2 ,
 wherein the fourth nitride semiconductor layer includes a first part, and a second part disposed on both sides of the first part and implanted with ions, and 
 wherein the mesa part includes the first part, and the side part includes the second part. 
 
     
     
       5. The semiconductor device according to  claim 4 , wherein the second part includes a doped layer implanted with the ions, and an undoped layer under the doped layer. 
     
     
       6. The semiconductor device according to  claim 4 , wherein the ions are ions of one of boron and nitrogen. 
     
     
       7. The semiconductor device according to  claim 2 , wherein the side part includes a layer subjected to contact processing with an insulating film. 
     
     
       8. The semiconductor device according to  claim 7 , wherein the insulating film is a nitride film. 
     
     
       9. The semiconductor device according to  claim 2 , wherein an end portion of the gate electrode is located over the side part. 
     
     
       10. The semiconductor device according to  claim 2 , further comprising a gate insulating film between the mesa part and the gate electrode. 
     
     
       11. A method of manufacturing a semiconductor device, comprising the steps of:
 (a) forming a second nitride semiconductor layer over a first nitride semiconductor layer; 
 (b) forming a third nitride semiconductor layer over the second nitride semiconductor layer; 
 (c) forming a fourth nitride semiconductor layer over the third nitride semiconductor layer; 
 (d) forming a mesa part including the fourth nitride semiconductor layer, and forming a side part including the fourth nitride semiconductor layer and provided on both sides of the mesa part; and 
 (e) forming a gate electrode above the mesa part and a first portion of the side part, 
 wherein a second portion of the side part extends to the outside of the gate electrode, and 
 wherein generation of two-dimensional electron gas between the second nitride semiconductor layer and the third nitride semiconductor layer is suppressed below the mesa part while being unsuppressed below the side part. 
 
     
     
       12. The method according to  claim 11 , wherein the step (d) is a step of providing the mesa part, and providing the side part having a smaller thickness than the mesa part on both sides of the mesa part. 
     
     
       13. The method according to  claim 11 , wherein the step (d) includes the steps of:
 (d1) forming a first mask film over a region of the fourth nitride semiconductor layer in which the mesa part is to be formed, and forming the side part by implanting ions with the first mask film as a mask; and 
 (d2) removing the first mask film, forming a second mask film larger than the region in which the first mask film has been formed over the fourth nitride semiconductor layer, and etching the fourth nitride semiconductor layer with the second mask film as a mask. 
 
     
     
       14. The method according to  claim 13 , wherein the side part includes a doped layer implanted with the ions, and an undoped layer under the doped layer. 
     
     
       15. The method according to  claim 13 , wherein the ions are ions of one of boron and nitrogen. 
     
     
       16. The method according to  claim 11 , wherein the step (d) includes the steps of:
 (d1) forming a first insulating film over a region of the fourth nitride semiconductor layer in which the mesa part is to be formed, and forming a second insulating film over the fourth nitride semiconductor layer as well as over the first insulating film, thereby forming a side part having a contact portion between the fourth nitride semiconductor layer and the second insulating film; and 
 (d2) forming a mask film over the fourth nitride semiconductor layer, the mask film being larger than the region in which the first insulating film has been formed, and etching the fourth nitride semiconductor layer with the mask film as a mask. 
 
     
     
       17. The method according to  claim 16 , wherein the second insulating film is a nitride film. 
     
     
       18. The method according to  claim 11 , wherein the mesa part includes the fourth nitride semiconductor layer being undoped. 
     
     
       19. The method according to  claim 11 , further comprising, between the step (d) and the step (e), the step of:
 (f) forming the gate insulating film over the mesa part, wherein the gate electrode is formed over the gate insulating film.